Aortic Stenosis

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Aortic stenosis is defined as an obstruction that impedes blood flow from the left ventricle to the aorta and is mostly secondary to aortic valvular disease. Other, less common etiologies of aortic stenosis include supravalvular and membranous subvalvular stenosis, which are generally congenital.

Aortic valvular stenosis is the most common valvular abnormality in the United States. It can be congenital, rheumatic, or calcific and degenerative. Calcific aortic valve stenosis is most prevalent in patients over 70 years of age (Fig. 27-14), whereas congenital, mostly bicuspid valve disease is more common in younger patients (Fig. 27-15). A bicuspid aortic valve leads to flow turbulence and valve trauma, which in return precipitates fibrosis, stiffness, and calcification. A third of bicuspid valves will become stenotic between the fourth and sixth decades of life and account for half of all surgical cases. Age-related calcific valves are affected by the same risk factors as in atherosclerosis, with inflammatory cells (macrophages, T lymphocytes), lipid and calcium deposits, and development of fibrosis. Rheumatic aortic valve stenosis is now uncommon in developed countries and is mediated by adhesion and the fusion of cusps.

The aortic valve surface area is normally 3.0 to 4.0 cm2. Symptoms typically do not appear unless the valve is narrowed to at least a fourth of its normal surface area. Stenosis is graded as mild (valve area >1.5 cm2), moderate (>1.0 to 1.5 cm2), or severe (<1 cm2) (Rahimtoola, 1989). The valve area narrows at an average rate of 0.12 cm2 per year (Otto et al., 1997). As the valve narrows, cardiac output remains stable at rest but diminishes with exercise. As disease progresses, LV mass increases and diastolic dysfunction becomes evident with an increase in LV filling pressure. Myocardial oxygen demand typically increases, and even in the absence of CAD, patients may experience angina. Patients with aortic stenosis have a good prognosis if they do not have symptoms of angina, CHF, or syncope/near-syncope, particularly with activity. Surgical management of the valve becomes necessary in symptomatic patients because of the increased incidence of sudden cardiac death.

Patients with severe aortic valve stenosis describe progressive dyspnea, chest pain and syncope with exertion, and symptoms of CHF, including orthopnea, paroxysmal nocturnal dyspnea, and edema. Syncope at rest is typically induced by arrhythmia. Patients with severe aortic valve stenosis have a 5% history of sudden cardiac death. In addition, these patients may give a history of rheumatic fever or rheumatic heart disease, transient ischemic attacks from calcium deposit systemic embolization, and intermittent GI bleeding from an increased incidence of arteriovenous malformations.

The typical physical signs of severe aortic valve stenosis are diminished carotid pulses (delayed and weak), a sustained apical impulse, a single second heart sound, an S4 gallop, and midsystolic crescendo-decrescendo murmur with late peaking best heard at the base of the heart, although in elderly patients it might be heard only at the apex.

Diagnostic tests include a chest radiograph, which could show a calcified valve, pulmonary venous congestion, or an increase in ascending aortic root size secondary to post-stenotic dilation. Also, a 12-lead ECG may show LVH and conduction abnormalities. An echocardio-gram typically confirms the diagnosis. Valve structure can be assessed, including the presence of calcification, reduction in cusp motion, and congenital abnormalities such as a bicuspid or abnormal tricuspid valve. A gradient can be measured across the valve (Fig. 27-16), and valve area can be determined using Doppler flow with reasonable accuracy (Currie et al., 1986). The presence of concomitant aortic valve insufficiency can also be visualized using color Doppler flow characteristics. Other important findings on echocardiography include the presence or absence of LVH and assessment of LV compliance, atrial size, and associated other valvular abnormalities. If noninvasive findings support the diagnosis of severe aortic stenosis and the patient is symptomatic, then diagnostic angiography is indicated to confirm the presence of severe aortic valve stenosis and assess the coronary arteries. Combined valve surgery and CABG can then be considered as indicated. Stress testing is absolutely contraindicated in the setting of symptomatic, severe aortic valve stenosis.

Figure 27-16 Velocity gradient across a calcified stenotic aortic valve, as seen with Doppler echocardiography.

Table 27-10 Prophylaxis for Bacterial Endocarditis*

Figure 27-16 Velocity gradient across a calcified stenotic aortic valve, as seen with Doppler echocardiography.

The treatment of aortic valve stenosis depends on the presence or absence of symptoms. Symptomatic, severe aortic valve stenosis carries a poor prognosis, with the average life expectancy of patients being 2 to 3 years (Ross and Braunwald, 1968). The 5- and 10-year mortality is approximately 52% to 80% and 80% to 90%, respectively (Horstkotte and Loogen, 1988; Turina et al., 1987). Aortic valve surgery with or without CABG is the treatment of choice (Lund, 1990; Schwarz et al., 1982). Aortic valvuloplasty carries a poor outcome and is reserved as a palliative therapy for inoperable patients. Typically, the improvement in the aortic valve gradient is mild with valvuloplasty, and a recurrence of severe stenosis can be expected within 6 months (Block and Palacios, 1988; Davidson et al., 1990). Surgery is typically not advised for asymptomatic severe valvular stenosis. Patients with dyspnea and indication of progressive LV dysfunction need to be considered for valve replacement. However, most patients with asymptomatic, severe aortic valve stenosis will develop symptoms within 5 years of follow-up. The 1-, 2-, and 5-year event-free probabilities were 80%, 63%, and 25%, respectively. Independent predictors of all-cause mortality include age, chronic renal failure, inactivity, and aortic valve velocity (Pellikka et al., 2005). A low threshold to intervene in patients with asymptomatic severe aortic stenosis needs to be considered, particularly when peak systolic velocity is 4.5 m/sec or greater on Doppler echocardiography, if associated with moderate or severe valvular calcification (Rosenheck et al., 2000).

Patients need to be advised on antibiotic prophylaxis to prevent endocarditis, especially with rheumatic valve disease (Dajani et al., 1997) (Table 27-10). Patients with moderate to severe aortic valve stenosis need to avoid moderate to severe physical exertion (Cheitlin et al., 1994). Arrhythmias need to be corrected promptly in patients with severe aortic stenosis. Follow-up echocardiography is indicated every year in patients with asymptomatic, severe aortic stenosis and every other year in those with moderate stenosis (Bonow et al., 1998).

Aortic valve replacement can be performed with a mechanical valve or a tissue valve depending on the clinical situation. For example, patients who have a contraindication to

Table 27-10 Prophylaxis for Bacterial Endocarditis*

Drug

Adult Dose

Pediatric Dose*

Time before Procedure

General Prophylaxis

Amoxicillin

2 g PO 2 g IV or IM

SO mg/kg PO SO mg/kg IM or IV

1 hour 30 minutes

Penicillin-Allergic Patients

Clindamycin

6OO mg PO

20 mg/kg PO

1 hour

Clarithromycin

SOO mg PO

15 mg/kg PO

1 hour

Azithromycin

SOO mg PO

15 mg/kg PO

1 hour

Clindamycin

6OO mg IV

20 mg/kg IV

30 minutes

Cefazolin

l g IV or IM

25 mg/kg IM or IV

30 minutes

From Dajani AS, Taubert KA, Wilson W, et al. Prevention of bacterial endocarditis: recommendations by the American Heart Association, Circulation 1997;96:358-366.

*Should not exceed adult dose

Figure 27-17 Aortic valve regurgitation, as seen with color Doppler echocardiography. Note the blue turbulent jet into the left ventricle in diastole.

anticoagulation with warfarin should receive a bioprosthetic valve. These valves typically do not require anticoagulation with warfarin, and patients generally receive only an aspirin subsequent to the procedure. Patients in their 60s or 70s with no contraindication to warfarin (Coumadin) are best served with mechanical valves because these last longer and may obviate the need for another valve surgery. Very elderly patients (80s) are typically given a tissue valve to obviate the need for anticoagulation. Antibiotic prophylaxis to prevent endocarditis is strongly recommended in patients with prosthetic valves.

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